JPH08286112A - Objective lens for microscope - Google Patents

Abstract

PURPOSE: To provide a dry system plan apochromat microscope objective lens which has a long operation distance although it has very high power and a high numerical aperture. CONSTITUTION: This objective lens consists of a 1st group G1 having a positive meniscus lens which has a concave surface on the object side, a 2nd group G2 which consists of a three-element cemented lens of a positive, a negative, and a positive lens and converges luminous flux, a 3rd group G3 including a cemented lens element arranged in the converged luminous flux, and a 4th group G4 which has a negative lens element having the concave surface on the object side, a concave surface on the image side as the most image-side lens surface, and negative refracting power on the whole, and satisfies a condition (1) of the curvature of the object-side concave surface of the most object- side lens, a condition (2) of the negative refracting power of the object-side cemented surface of the three-element cemented lens, a condition (3) of the positive refracting power of the 2nd group G2 on the most image-side surface, and a condition (4) of the sum of the absolute values of refracting power of the 2nd group G2 on the cemented surface and the most image-side surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry microscope objective lens used for inspection of IC wafers and the like, and more particularly to an ultra-high magnification plan apochromat microscope having a magnification of about 150 ×, a large numerical aperture and a long working distance. The present invention relates to an objective lens.

[0002]

2. Description of the Related Art At present, the degree of integration of semiconductors is increasing year by year, and patterns are becoming finer. For this reason, a fine structure cannot be sufficiently observed with a conventional objective lens of about 100 ×.
Therefore, there is a demand for an objective lens with a higher magnification.

However, in general, when observing with the human eye, the upper limit is a total magnification of about 100 times the numerical aperture (NA) of the objective lens. This is because with a general observation method, even if the magnification is further increased, a blurred image is observed, and a fine pattern cannot be recognized. Therefore, when a standard 10 × eyepiece is used, it has been considered that 100 × is the limit for a dry microscope objective lens whose NA does not exceed 1. Obviously, if the space between the sample and the objective lens is filled with oil or the like to raise the NA, the magnification can be further increased for observation, but immersion in oil is not appropriate for a sample such as a semiconductor.

According to the above idea, a magnification of more than 100 × is an invalid magnification, but this can be said in the naked eye observation, and in the inspection using the TV device or the image analysis,
Since the resolution of the image sensor is low, it is necessary to increase the magnification in order to obtain a resolution similar to that observed with the naked eye. Further, it has been found that by performing illumination with increased coherence, it is possible to perform contrast observation on a fine pattern that could not be conventionally observed due to insufficient contrast.

Under these circumstances, recently, 150 ×
The demand for the above ultra-high magnification microscope objective lens is increasing.
Since the ultra-high magnification microscope objective lens is for inspecting a fine pattern, it is naturally required to be an apochromat. A microscope objective lens that is not an apochromat has a poor resolution and cannot observe a fine pattern. In addition, a microscope objective lens having a long working distance is required from the viewpoint of safety and operability. A lens with a short working distance has a possibility of contaminating or scratching the sample, and requires careful handling, so the operability is poor.

However, increasing the magnification and increasing the working distance significantly deteriorates the chromatic aberration and the spherical aberration, which makes it very difficult to design. This is because it is necessary to shorten the focal length of the objective lens in order to increase the magnification, which increases the power of each lens surface and increases the amount of aberration generated. In addition, when trying to increase the working distance, the luminous flux incident on the lens becomes large. Therefore, in order to converge this luminous flux with a limited total length, it is necessary to increase the power of each lens surface. In addition, the amount of aberration generated increases. If the entire length of the microscope objective lens is increased, the bending of the light beam on each lens surface can be reduced, so that the amount of aberration can be suppressed and the working distance can be increased. It lacks general versatility and is not very general.

Among the conventional microscope objective lenses, Japanese Patent Publication No.
-No. 26446 has a magnification of 150x to 200x
With high magnification, NA is as large as 0.95, and chromatic aberration is well corrected. However, the working distance is only 0.4 mm,
Operability is very poor. The working distance of 0.4 mm is only 0.3 to 0.4 times the focal length of the objective lens.

There are the following inventions with a magnification of about 100 ×. Japanese Examined Patent Publication No. 4-26447 has a magnification of 1
The invention discloses that the working distance is 2.3 mm at 00 ×, NA 0.85, or the working distance is 2.9 mm at NA 0.8. In the former, the working distance is only about 1.1 times the focal length of the objective lens, and in the latter, the working distance is about 1.4 times the focal length of the objective lens, but the NA is only 0.8, which is very small. It is still insufficient to observe the structure.

Japanese Patent Publication No. 3-58493 has a magnification of 100.
The invention of x, NA 0.9, and working distance 0.75 mm is described. However, the working distance of 0.75 mm is further shortened when converted into a mechanical working distance, which is not sufficient as a working distance of a microscope objective lens of high magnification. In addition, 0.75m
m is only about 0.8 times the focal length of the objective lens.

Japanese Patent Laid-Open No. 4-220616 discloses a magnification of 10
The invention of 0x, NA 0.9, working distance 2.48 mm is described. This objective lens has a high NA,
Has a long working distance. However, it is necessary to have a length more than twice the total length of a normal microscope objective lens, and it cannot be used except for a special microscope, and its versatility is very poor.

Japanese Patent Laid-Open No. 4-40409 discloses a magnification of 100.
×, NA 0.8, working distance 4.77 mm, or
A microscope objective with an NA of 0.75 and a working distance of 5.3 mm is described. However, with NA 0.8,
Insufficient for observing fine structures.

The above four inventions are microscope objective lenses of about 100 ×, and it is difficult to construct a microscope objective lens of higher magnification in terms of lens configuration.

Although it is different from the specification of the present invention, Japanese Patent Laid-Open No. 4-7
No. 0618 has a larger magnification of 250 ×, NA
A microscope objective having a long working distance of 0.9 and a working distance of 0.67 mm to 1.25 mm is described. However, in order to achieve the magnification of 250 ×, the lens structure is very complicated.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the problems of the prior art as described above, and an object thereof is ultra-high magnification and high numerical aperture, and long working distance and drying. System plan apochromat microscope objective lens.

[0015]

A microscope objective lens of the present invention which achieves the above object comprises a first lens group G having, in order from the object side, a positive meniscus lens having a concave surface facing the object side.
1. A second lens group G2 including a three-lens cemented lens including a positive lens, a negative lens, and a positive lens, which makes a light beam a convergent light beam, a third lens group G3 having a cemented lens component arranged in the convergent light beam, the object side Is characterized by having a negative lens component with a concave surface facing toward, a lens surface closest to the image side being a concave surface toward the image side, and consisting of a fourth lens group G4 having a negative refracting power as a whole, and satisfying the following condition: It is what _{(1) | R A |>} | R B | (2) (N B -N A) | H 1 | / | R C |> 0.1 (3) (N C -1) | H 2 | / | R _D |> 0.24 (4) 0.36 <(N _B −N _A ) | H ₁ | / | R _C |
_{+ (N C -1) | H} 2 | / | R D | <0.53 However, R _A, the object side of the most object side positive meniscus lens of the R _B are each in the first lens group G1, the image side surface , N _A , N _B , and N _C are the refractive indices of the object-side positive lens, the negative lens, and the image-side positive lens of the second lens group G2, R
_C and H ₁ are the radius of curvature of the object-side cemented surface of the second lens group G2 and the ray height at which the ray of the maximum numerical aperture at that cemented surface passes,
R _D and H ₂ are the ray heights through which the rays having the maximum radius of curvature on the surface closest to the image side of the second lens group G2 and the maximum numerical aperture on that surface pass.

In this case, it is desirable to satisfy the following conditions. (5) ν _A −ν _B > 30 (6) ν _C −ν _B > 30 where ν _A , ν _B , and ν _C are the second lens group G2, respectively.
Are the Abbe numbers of the object-side positive lens, the negative lens, and the image-side positive lens.

Furthermore, it is desirable to have a cemented meniscus lens having a convex surface facing the object side in the third lens group G3 and satisfy the following conditions. (7) ν _D <ν _E where ν _D and ν _E are positive lenses of a cemented meniscus lens whose convex surface faces the object side in the third lens group G3,
It is the Abbe number of a negative lens.

[0018]

The reason why the above structure is adopted and its function will be described below. First, the divergence angle of a high NA ray emerging from an object is gradually reduced by the first lens group having a positive meniscus lens facing the concave surface on the object side.

Generally, when the working distance is short, the Petzval sum is corrected by giving a strong curvature to the object-side concave surface of the lens closest to the object. However, if the working distance is long,
If the curvature of the concave surface on the object side remains strong, the angle of incidence of the light ray incident on this surface becomes small, and therefore the bending of the light ray becomes small. Therefore, the light rays cannot be sufficiently converged on the first lens surface, a large refractive power is required on the lens surfaces that follow, and the amount of spherical aberration generated increases in the entire system. Therefore, in order to achieve a long working distance, the curvature of the object-side concave surface of the most object-side lens needs to satisfy the conditional expression (1). If this condition is exceeded and the radius of curvature of the image-side surface becomes larger than that of the object-side surface, this is advantageous for correcting Petzval sum, but the bending of light rays on the lens surface on the object side becomes smaller, so A large refractive power is required for the surface, and the amount of aberration generated increases as a whole.

Next, the second lens group has a function of converting the light beam gradually bent by the first lens group into a convergent light beam. Generally, the higher the magnification of the lens system,
Further, as the working distance increases, it becomes more difficult to correct spherical aberration and chromatic aberration of the lens. With an objective lens such as the present invention, it is usually difficult to correct these aberrations because the magnification is very large and the working distance is also very large. Therefore, by using three cemented lenses, a positive lens, a negative lens, and a positive lens, in the second lens group having the highest ray height, the chromatic aberration performance is greatly improved.

Further, as in the condition of the above equation (2),
By making great use of the negative refracting power of the cemented surface on the object side of the three-lens cemented lens, spherical aberration is satisfactorily corrected, and
By raising the ray height, it is easy to correct aberrations in the rear lens group. The condition of the formula (2) is not satisfied, and the lower limit of 0.1 is satisfied.
If it exceeds, spherical aberration and axial chromatic aberration will be undercorrected and the performance will deteriorate. Further, the height of the light ray incident on the third lens group is not so high that the negative refractive power at the cemented surface of the third lens group cannot be increased. If the negative refracting power at the cemented surface of the third lens group is increased while the ray height is low, a large positive refracting power is required to convert the ray into a convergent light beam, and spherical aberration is undercorrected as a whole. . In the case where it is difficult to give the cemented surface of the third lens group a sufficient negative refractive power, it is desirable to further satisfy the following conditional expression.

(2 ′) (N _B −N _A ) | H ₁ | / | R _C |> 0.13 The condition of the above expression (3) is that the positive refraction on the most image side surface of the second lens group is Represents power. If this condition is not satisfied, the lower limit of 0.2
When it exceeds 4, the converging action in the second lens group is weakened, and instead, a large positive refractive power is required in the third lens group. As a result, the angle of the light ray incident on the fourth lens group becomes steep, and strong negative power for diverging the light ray is required for the fourth lens group, so that the aberration amount of each group becomes large and aberration correction is performed. It will be difficult.

The condition of the above formula (4) is a condition of the sum of the absolute values of the negative refractive power of the cemented surface of the second lens group and the positive refractive power of the surface closest to the image side. If the lower limit of 0.36 in the expression (4) is not satisfied, the refraction of light rays in the second lens group becomes small, and sufficient power for correcting aberration cannot be obtained. On the other hand, when the upper limit of 0.53 is exceeded, the amount of aberration generated on each surface becomes too large, which exceeds the correction limit.

As described above, according to the present invention, various aberrations are satisfactorily corrected by using three cemented lenses of positive, negative, and positive in the second lens group. Aberration and axial chromatic aberration are undercorrected, and ultra high magnification,
Long working distance cannot be achieved.

The third lens group, which includes the cemented lens component and is arranged in the convergent light beam, has a function of correcting chromatic aberration that cannot be completely removed by the second lens group. Therefore, three well-known lenses are used. It is desirable to have a cemented lens.
In addition to chromatic aberration, it also functions to favorably correct spherical aberration, coma and astigmatism.

The fourth lens group has a function of diverging a convergent light beam and guiding it to an image by a negative lens component having a concave surface facing the object side. Further, by making the lens surface closest to the image side concave on the image side, a negative Petzval sum is generated and the flatness of the image surface is corrected.

In the microscope objective lens of the present invention described above, it is more desirable if the following conditions (5), (6) and (7) are satisfied. (5) ν _A −ν _B > 30 (6) ν _C −ν _B > 30 (7) ν _D <ν _E where ν _A , ν _B , and ν _C are the second lens group G2, respectively.
Abbe numbers of the object-side positive lens, the negative lens, and the image-side positive lens, ν _D and ν _E are the positive and negative Abbe numbers of the cemented meniscus lens with the convex surface facing the object side in the third lens group G3, respectively. Is.

The above expressions (5) and (6) are conditions for favorably correcting chromatic aberration in the second lens group. (5),
By increasing the difference in Abbe number between the positive lens and the negative lens as in the expression (6), chromatic aberration can be favorably corrected.
In order to satisfactorily correct the secondary spectrum, a glass material having extraordinary dispersion may be used for these three lenses.

The above expression (7) is a condition for favorably correcting off-axis chromatic aberration in the fourth lens group. If this condition is not satisfied and the Abbe number of the positive lens becomes larger than the Abbe number of the negative lens, it becomes difficult to balance on-axis and off-axis chromatic aberration.

[0030]

EXAMPLES Examples 1 to 3 of the microscope objective lens of the present invention will be described below. The lens data of each example will be described later, but FIGS. 1, 2 and 3 show examples 1, 2 and 3, respectively.
It is sectional drawing which shows the lens structure of 3.

Regarding the constitution of each group of the first embodiment, the first lens group G1 is composed of two single positive meniscus lenses with the concave surface facing the object side, and the second lens group G2 is a biconvex lens and a biconcave lens. The third lens group G3 includes three biconvex lenses, a negative meniscus lens cemented with a concave surface facing the object side, and a biconvex lens and biconcave lens cemented meniscus lens. ,
The fourth lens group G4 includes a biconcave lens, and a cemented lens of a positive meniscus lens having a concave surface facing the object side and a biconcave lens.

With respect to the configuration of each group in Example 2, the first lens group G1 is composed of a single positive meniscus lens having a concave surface facing the object side and a plano-convex lens having a flat surface facing the object side. The lens group G2 includes a double-convex lens, a double-concave lens, and a double-convex cemented lens, and a third lens group G3.
Is a cemented lens made up of a biconvex lens and a negative meniscus lens having a concave surface facing the object side, a negative meniscus lens having a concave surface facing the image side, and a biconvex lens, and a negative meniscus lens having a concave surface facing the object side. , A biconvex lens and a cemented meniscus lens of a biconcave lens, and a fourth lens group G4
Is composed of a biconcave lens, and a cemented lens of a plano-concave lens and a plano-concave lens having a flat surface facing the image side.

Regarding the constitution of each group of the third embodiment, the first lens group G1 is composed of two single positive meniscus lenses with the concave surface facing the object side, and the second lens group G2 is a biconvex lens and a biconcave lens. The third lens group G3 includes a cemented lens of a biconvex lens and a negative meniscus lens having a concave surface facing the object side, a negative meniscus lens having a concave surface facing the image side, and a biconvex lens. The fourth lens group G4 includes a double-concave negative meniscus lens cemented lens with a concave surface facing the object side, and a double-concave and double-concave lens cemented meniscus lens. It consists of a lens and a cemented lens of a plano-concave lens.

In each embodiment, the magnification is 150 ×, NA0.
9 and super high magnification, high NA, and working distance,
In Example 1, a long working distance of 1.36 times the focal length of the objective lens, in Example 2 was 1.55 times, and in Example 3 was 1.48 times.

The lens data of each embodiment will be shown below. In addition to the above, the symbol is f, the focal length of the objective lens, and N.
A is the numerical aperture, β is the magnification, and WD is the working distance. Also,
r ₁ , r ₂ ... Is the radius of curvature of each lens surface shown in order from the object side, d ₁ , d ₂ ... Is the distance between the lens surfaces shown in order from the object side, and n _d1 , n _d2 ... Is from the object side. The d-line refractive index of each lens, ν _d1 , ν _d2 ... _{Shown in} order is the Abbe number of each lens shown in order from the object side.

Example 1 f = 1.2, NA = 0.9, β = 150, WD = 1.637 r ₁ = -4.8153 d ₁ = 3.0600 n _d1 = 1.74100 ν _d1 = 52.65 r ₂ = -3.7601 d ₂ = 0.1000 r ₃ = -84.8138 d ₃ = 2.4600 n _d2 = 1.56907 ν _d2 = 71.30 r ₄ = -9.5427 d ₄ = 0.1000 r ₅ = 11.3685 d ₅ = 4.5000 n _d3 = 1.43875 ν _d3 = 94.97 r ₆ = -9.0634 d ₆ = 1.6000 n _d4 = 1.72600 ν _d4 = 53.57 r ₇ = 24.9477 d ₇ = 4.6500 n _d5 = 1.43875 ν _d5 = 94.97 r ₈ = -10.1258 d ₈ = 0.1000 r ₉ = 17.8509 d ₉ = 5.2500 n _d6 = 1.43875 ν _d6 = 94.97 r ₁₀ = -8.8561 d ₁₀ = 1.0000 n _d7 = 1.61340 ν _d7 = 43.84 r ₁₁ = -32.7446 d ₁₁ = 0.2000 r ₁₂ = 24.0740 d ₁₂ = 3.6000 n _d8 = 1.43875 ν _d8 = 94.97 r ₁₃ = -8.6667 d ₁₃ = 1.0000 n _d9 = 1.64450 ν _d9 = 40.82 r ₁₄ = -36.3396 d ₁₄ = 0.1000 r ₁₅ = 12.5940 d ₁₅ = 4.0000 n _d10 = 1.43875 ν _d10 = 94.97 r ₁₆ = -8.0348 d ₁₆ = 1.0000 n _d11 = 1.74000 ν _d11 = 31.71 r ₁₇ = -90.7321 d ₁₇ = 0.7600 r ₁₈ = 15.8159 d ₁₈ = 3.1600 n _d12 = 1.761 82 ν _d12 = 26.55 r ₁₉ = -7.8535 d ₁₉ = 0.8000 n _d13 = 1.80610 ν _d13 = 40.95 r ₂₀ = 18.5376 d ₂₀ = 4.1900 r ₂₁ = -3.5477 d ₂₁ = 0.8000 n _d14 = 1.51633 ν _d14 = 64.15 r ₂₂ = 67.4681 d ₂₂ = 0.6400 r ₂₃ = -6.8723 d ₂₃ = 1.5000 n _d15 = 1.78472 ν _d15 = 25.71 r ₂₄ = -2.7221 d ₂₄ = 0.8000 n _d16 = 1.53996 ν _d16 = 59.57 r ₂₅ = 9.6162 R _A = -4.8153 R _{B = -3.7601 N A = 1.43875 ν A} = 94.97 N B = 1.726 ν B = 53.57 N C = 1.43875 ν C = 94.97 R C = -9.0634 R D = -10.1258 H 1 = 5.84 H 2 = 6.5 ν D = 26.55 ν _{E = 40.95 (1) | R} A |> | R B | (2) (N B -N A) | H 1 | / | R C | = 0.19 (3) (N C -1) | H 2 | / _{| R D | = 0.28 (4} ) (N B -N A) | H 1 | / | R C | + (N C -
1) | H ₂ | / | _RD || 0.47 (5) ν _A −ν _B = 41.4 (6) ν _C −ν _B = 41.4 (7) ν _D <ν _E
.

Example 2 f = 1.2, NA = 0.9, β = 150, WD = 1.86 r ₁ = -3.9188 d ₁ = 2.1900 n _d1 = 1.88300 ν _d1 = 40.78 r ₂ = -3.2806 d ₂ = 0.1100 r ₃ = ∞ d ₃ = 2.6300 n _d2 = 1.56907 ν _d2 = 71.30 r ₄ = -11.2366 d ₄ = 0.1200 r ₅ = 12.1870 d ₅ = 3.8000 n _d3 = 1.43875 ν _d3 = 94.97 r ₆ = -10.2129 d ₆ = 1.0000 n _d4 = 1.64450 ν _d4 = 40.82 r ₇ = 11.2157 d ₇ = 5.3500 n _d5 = 1.49700 ν _d5 = 81.61 r ₈ = -11.2157 d ₈ = 0.1500 r ₉ = 10.6293 d ₉ = 5.7400 n _d6 = 1.43875 ν _d6 = 94.97 r ₁₀ =- 10.3968 d ₁₀ = 1.3500 n _d7 = 1.75500 ν _d7 = 52.33 r ₁₁ = -33.7903 d ₁₁ = 0.2500 r ₁₂ = 14.3932 d ₁₂ = 1.2000 n _d8 = 1.74000 ν _d8 = 31.71 r ₁₃ = 5.6196 d ₁₃ = 5.4800 n _d9 = 1.43875 ν _d9 = 94.97 r ₁₄ = -5.3801 d ₁₄ = 1.1000 n _d10 = 1.74000 ν _d10 = 31.71 r ₁₅ = -19.1219 d ₁₅ = 2.7400 r ₁₆ = 7.2843 d ₁₆ = 3.0400 n _d11 = 1.78472 ν _d11 = 25.68 r ₁₇ =- 5.7970 d ₁₇ = 0.9000 n _d12 = 1.88300 ν _d12 = 40.78 r ₁₈ = 7.0454 d ₁₈ = 4.4800 r ₁₉ = -4.4881 d ₁₉ = 0.8000 n _d13 = 1.51633 ν _d13 = 64.15 r ₂₀ = 17.4174 d ₂₀ = 0.6100 r ₂₁ = 5.0346 d ₂₁ = 1.5000 n _d14 = 1.74000 ν _d14 = 31.71 r ₂₂ = ∞ d _{22 = 0.6000 n d15 = 1.72916 ν d15} = 54.68 r 23 = 4.9962 R A = -3.9188 R B = -3.2806 n A = 1.43875 ν A = 94.97 n B = 1.6445 ν B = 40.82 n C = 1.497 ν C = 81.61 R C _{= -10.2129 R D = -11.2157 H 1} = 5.47 H 2 = 6.06 ν D = 25.68 ν E = 40.78 (1) | R A |> | R B | (2) (N B -N A) | H 1 | _{/ | R C | = 0.11 (} 3) (N C -1) | H 2 | / | R D | = 0.27 (4) (N B -N A) | H 1 | / | R C | + (N C −
1) | H ₂ | / | _RD || 0.38 (5) ν _A −ν _B = 54.15 (6) ν _C −ν _B = 40.79 (7) ν _D <ν _E
.

Example 3 f = 1.2, NA = 0.9, β = 150, WD = 1.78 r ₁ = -4.2286 d ₁ = 2.3200 n _d1 = 1.88300 ν _d1 = 40.78 r ₂ = -3.5839 d ₂ = 0.1100 r ₃ = -17.9868 d ₃ = 2.6900 n _d2 = 1.56907 ν _d2 = 71.30 r ₄ = -6.4513 d ₄ = 0.1200 r ₅ = 16.6330 d ₅ = 4.9600 n _d3 = 1.43875 ν _d3 = 94.97 r ₆ = -6.7429 d ₆ = 1.4000 n _d4 = 1.64450 ν _d4 = 40.82 r ₇ = 36.4383 d ₇ = 4.7900 n _d5 = 1.49700 ν _d5 = 81.61 r ₈ = -9.6810 d ₈ = 0.1500 r ₉ = 13.0785 d ₉ = 5.3900 n _d6 = 1.43875 ν _d6 = 94.97 r ₁₀ = -9.7593 d ₁₀ = 1.3500 n _d7 = 1.75500 ν _d7 = 52.33 r ₁₁ = -25.8225 d ₁₁ = 0.2500 r ₁₂ = 18.5014 d ₁₂ = 1.2000 n _d8 = 1.74000 ν _d8 = 31.71 r ₁₃ = 6.4825 d ₁₃ = 4.7200 n _d9 = 1.43875 ν _d9 = 94.97 r ₁₄ = -7.9108 d ₁₄ = 1.1000 n _d10 = 1.74000 ν _d10 = 31.71 r ₁₅ = -21.2552 d ₁₅ = 2.7400 r ₁₆ = 7.4953 d ₁₆ = 3.0400 n _d11 = 1.76182 ν _d11 = 26.52 r ₁₇ = -5.6936 d ₁₇ = 0.9000 n _d12 = 1.88300 ν _d12 = 40.78 r ₁₈ = 7.0138 d ₁₈ = 4.4800 r ₁₉ = -4.3215 d ₁₉ = 0.8000 n _d13 = 1.51633 ν _d13 = 64.15 r ₂₀ = 12.2169 d ₂₀ = 0.6100 r ₂₁ = 4.3393 d ₂₁ = 1.5000 n _d14 = 1.74000 ν _d14 = 31.71 r ₂₂ = ∞ d _{22 = 0.6000 n d15 = 1.72916 ν d15} = 54.68 r 23 = 4.0997 R A = -4.2286 R B = -3.5839 n A = 1.43875 ν A = 94.97 n B = 1.6445 ν B = 40.82 n C = 1.497 ν C = 81.61 R C _{= -6.7429 R D = -9.681 H 1} = 5.46 H 2 = 6.61 ν D = 26.52 ν E = 40.78 (1) | R A |> | R B | (2) (N B -N A) | H 1 | _{/ | R C | = 0.17 (} 3) (N C -1) | H 2 | / | R D | = 0.34 (4) (N B -N A) | H 1 | / | R C | + (N C −
_{1) | H 2 | / |} R D | = 0.51 (5) ν A -ν B = 54.15 (6) ν C -ν B = 40.79 (7) ν D <ν E
.

In each of Examples 1 to 3 described above, the infinity correction type objective lens in which the light emitted from the objective lens becomes a parallel light beam, and it does not form an image by itself. Therefore, for example, it is used in combination with an imaging lens having the lens data shown below and showing the lens cross section in FIG. However, in the lens data, r ₁ ′, r ₂ ′ ... Are the radii of curvature of the respective lens surfaces shown in order from the object side, d ₁ ′, d ₂ ′ ... are the intervals between the lens surfaces shown in order from the object side, n _d1 ', n _d2 ' ... are d-line refractive indices of the lenses shown in order from the object side, and v _d1 ', v _d2 ' ... are Abbe numbers of the lenses shown in order from the object side.

R ₁ '= 68.7541 d ₁ ' = 7.7321 n _d1 '= 1.48749 ν _d1 ' = 70.20 r ₂ '= -37.5679 d ₂ ' = 3.4742 n _d2 '= 1.80610 ν _d2 ' = 40.95 r ₃ '= -102.8477 d ₃ '= 0.6973 r ₄ ' = 84.3099 d ₄ '= 6.0238 n _d3 ' = 1.83400 ν _d3 '= 37.16 r ₅ ' = -50.7100 d ₅ '= 3.0298 n _d4 ' = 1.64450 ν _d4 '= 40.82 r ₆ ' = 40.6619.

In this case, the distance between the objective lenses of Examples 1 to 3 and the imaging lens of FIG. 4 may be any position between 50 mm and 170 mm, but Example 1 when this distance is 119 mm Aberration diagrams of 3 to 3 are shown in FIGS. 5 to 7, respectively. However, in these aberration diagrams, (a) shows spherical aberration, (b) shows distortion, (c) shows astigmatism, and (d) shows coma. In these aberration diagrams, IM. H indicates the image height. In addition, if the above-mentioned interval is between 50 mm and 170 mm, 11
Almost the same aberration situation is shown at positions other than 9 mm.

[0042]

As is apparent from the above description, the microscope objective lens of the present invention has an ultra-high magnification of about 150 ×, a long working distance, and a high resolution and good visibility.
It is a lens system suitable for observing a wafer sample or the like.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view of a first example of a microscope objective lens according to the present invention.

FIG. 2 is a lens cross-sectional view of Example 2.

FIG. 3 is a lens cross-sectional view of Example 3.

FIG. 4 is a lens cross-sectional view of an example of an imaging lens used with the microscope objective lens of each example.

FIG. 5 is an aberration diagram showing spherical aberration, distortion, astigmatism, and coma of Example 1.

FIG. 6 is an aberration diagram showing spherical aberration, distortion, astigmatism, and coma of Example 2.

FIG. 7 is an aberration diagram showing spherical aberration, distortion, astigmatism, and coma of Example 3.

[Explanation of symbols]

 G1 ... First lens group G2 ... Second lens group G3 ... Third lens group G4 ... Fourth lens group

Claims (3)

[Claims] 1. A first lens group G1 having a positive meniscus lens having a concave surface facing the object side in order from the object side, and a triplet cemented lens including a positive lens, a negative lens, and a positive lens, wherein the light beam is a convergent light beam. A second lens group G2, a third lens group G3 having a cemented lens component arranged in the convergent light beam, a negative lens component having a concave surface facing the object side, and the most image-side lens surface is a concave surface facing the image side. A microscope objective lens characterized by comprising a fourth lens group G4 having a negative refracting power as a whole and satisfying the following conditions. _{(1) | R A |>} | R B | (2) (N B -N A) | H 1 | / | R C |> 0.1 (3) (N C -1) | H 2 | / | R _D |> 0.24 (4) 0.36 <(N _B −N _A ) | H ₁ | / | R _C |
_{+ (N C -1) | H} 2 | / | R D | <0.53 However, R _A, the object side of the most object side positive meniscus lens of the R _B are each in the first lens group G1, the image side surface , N _A , N _B , and N _C are the refractive indices of the object-side positive lens, the negative lens, and the image-side positive lens of the second lens group G2, R
_C and H ₁ are the radius of curvature of the object-side cemented surface of the second lens group G2 and the ray height at which the ray of the maximum numerical aperture at that cemented surface passes,
R _D and H ₂ are the ray heights through which the rays having the maximum radius of curvature on the surface closest to the image side of the second lens group G2 and the maximum numerical aperture on that surface pass. 2. The microscope objective lens according to claim 1, which satisfies the following condition. (5) ν _A −ν _B > 30 (6) ν _C −ν _B > 30 where ν _A , ν _B , and ν _C are the second lens group G2, respectively.
Are the Abbe numbers of the object-side positive lens, the negative lens, and the image-side positive lens. 3. The microscope objective lens according to claim 1, wherein a cemented meniscus lens having a convex surface facing the object side is provided in the third lens group G3, and the following condition is satisfied. (7) ν _D <ν _E where ν _D and ν _E are positive lenses of a cemented meniscus lens whose convex surface faces the object side in the third lens group G3,
It is the Abbe number of a negative lens.